Acrylonitrile process



Patented Dec. 14, 1948 ACRYLONITRILE rnocnss Harold Wilfred Arnold, Wilmington, DeL, assignor to E. I. du Pont' de Ncmours & Company, Wilmington, Del., a corporation of Delaware No Drawing. Application August 9, 1944,

- Serial No. 548,782

'3 Claims. (01. zoo-s3) This invention relates to polymers of monounsaturated compounds and to a method for 1mproving certain properties of these polymers. More specifically, it relates to a method for con-.. trolling and improving the film and fiber properties of polymers and copolymers produced from acrylonitrile.

Polyacrylonitrile and certain copolymers containing predominant amounts of combined acrylonitrile have been spun by adaptations of wet or dry processes to exceptionally strong fibers which show excellent outdoor durability and chemical resistance. Because of their high strength it has been desired to employ these fibers in the carcasses of heavy-duty truck tires and aircraft tires, in cordage, and in other applications which require high strength fibers whose tenacity is not greatly decreased at the elevated temperatures which may be developed during normal usage. Fibers from polyacrylonitrile which has been polymerized in a conventional manner have not been acceptable because of the decrease in tenacity at high temperatures.

This invention has as an object the provision of a practical means for producing a very substantial improvement in the high temperature durability of films and fibers of polyacrylonitrile or copolymers containing predominant amounts of combined acrylonitrile. Other objects will appear hereinafter.

These objects are accomplished by the following invention wherein acrylonitrile either alone or in mixture with not more than 10% of at least one other copolymerizable monoethylenic compound is polymerized by any polymerization process in the presence of a monomeric dithioglycidol,

- e. g., dithioglycidol,

A mixture of 1000 parts of distilled water, 100

' parts of acrylonitrile, and 0.1 part of dithioglywhich may be prepared by the process of Signaigo Serial No. 498,879, filed September 20, 1943, is stirred in a vessel whose temperature is maintained at 35 C. Nitrogen is passed slowly over the surface of the liquid during the polymerization. A catalyst mixture consisting of one part of ammonium perdisulfate and 0.3 part of sodium. bisulfite is added and the mixture thereafter stirred at 35 C. for 18 hours. The resulting polymer slurry is steamed to remove unpolymerized monomer and' the polymer filtered, washed thoroughly with several changes of water, and dried at 30 C. The dried polymer amounts to '71 parts.

In an exactly analogous operation, except that the dithioglycidol is omitted, acrylonitrile is polymerized alone to give an 83% yield of polymer. The following table shows a comparison of certain of the properties of the modified and unmodified products. Tests are carried out on films which have been cast from 10% solutions in dimethyl formamide on glass surfaces heated to -90" C., stripped and heated at 80 C. for four hours and thereafter extracted with boiling water for thirty minutes to remove traces of residual. dimethyl formamide.

The molecular weights here recorded are determined from viscosity measurements of 01% solutions in d1- methyl formamidc, using the relationship C IunJil where nsp= specificviscosity, C=tl1e concentration in niols of monomer unit per liter of solution. and Km is a constant whose value is 1.5X10- The Staudinger equation in the above form is subject to a number of limitations and in the case of polyacrylonitrile the value of Km is at best only an approximation. However, the molecular weights recorded above are valid for comparative purposes.

The sticking temperature is determined on strips of film 0.3 inch wide and 0.001 inch thick by suspending the film over a brass block under sufficient tension to keep it about 4 inch above the block. The block is heated at a rate of about 5 per minute and when the temperature reaches 120 C. the sample is brought into contact with the block under a 200 gram load for ten seconds. This procedure is repeated with every 5 rise in temperature until the point is reached at which the film fails to pull away from the block after the removal of the weight. This point is designated as the sticking temperature. Dur ing the intervals in which the sample is not in contact with the block an asbestos shield is placed between the block and the sample to minimize heat radiation.

Determinations of tensile strength/elongation are carried out on a Model X3 tester. manufactured by the Henry L. Scott (30., on films which have been stretched 1000% at (3., set under tension at 140 C. and relaxed at C.

EXAMPLE II consists of one part of ammonium perdisulfate and 05 part of sodium bisulfite. The reaction 40 is interrupted at the conclusion of 2% hours and and relaxed as in Example I.

a,4se,seo

the polymer isolated as in Example 1. giving a yield of 79 parts. A duplicate experiment in which the dithloglycidol is replaced by 0.45% dodecyl mercaptan gives a yield of 82% of polymer in 2.5 hours. The following table compares the properties of films oi the unmodified acrylo nitrlle polymer with those modified by dodecyl mercaptan and dithioslycidol. All tests are carried out on films which have been stretched, set,

Table II hoxylic acids or their anhydrides or derivatives such as-diethyl iumarate, diethyl maleate, diethyl cltraconate, diethyl mesaconate; styrene, vinylniphthalene, and the like. For the purpose of this application, the copolymerization comonomers are those which undergo polymerization to the extent of at least 50% ot the original mono Modifier 3,: $2

BRIDE.

mung I sile Sgggth cen iiidu'aa'i'e'wi ogy o Dodecyl meroaptan (0.45%)

Per sent I The temperature at elongation is determined by suspending the film in a well insulated. electrically heated chamber a t under a load corresponding to one gram per denier. Heat is now proximately 16 minutes are required to raise the temperature from 25 C. to 150 e inflection point of the elongation-temperature curve occurs at approximately 25%elongat1on. This temapplied at such rate that C. It has been found that graturo corresponds to a thermal yield point and is useful in comparing various samples of polyam'ylonltrile.

eating is continued beyond the theme] per cent elongation at break are recorded l The determination of the variation in tus used in the determination of the temperature at 26% elongation. In

between the grips and held without tension until temperature equilibrium is established. Tb is yield point until breakage occurs-and the break temperature and tensile strength with temperature is likewise carried out in the apparathe test the sample is attached a temperature regulated by means of a Variac or similar variable resistance. A load is then applied in gradually increasin amounts, at a re of 10 tlon in tensile strength with tem perature modified polyacrylonitrile is illustraed by is 86% oi the tensile strength at 25 Exnsrum molecular weight.

In this invention dithioglycidols are used as modifiers or control agents in the polymerization of acrylonitrile either alone or in mixtures containing notmore than 10% of at least one monoethylenically unsaturated compound which is copolymerizable with acrylouitrile. Such compounds include acrylic, alpha-chloroacrylic and methacrylic acids; methyl methacrylate, ethyl; methacrylate, butyl methaczylate, octyl methacrylate, 2-nitro-2-rnethylpropyl methacrylate. rhethoxymethyl methacrylate, p-chloroethyl methacrylate, and the corresponding esters of acrylic and alpha-chloroacrylic acids; vinyl chloride, vinyl fluoride, vinyl bromide, vinylidene chloride, 1-chloro1-bromoethylene, vinylidene' bromide, l-fluoro-l-chlcroethylene, Ll-difluoroethylene; methacrylonitrlle, alpha-chloroacrylonl trlle; acrylamide, methacrylamlde, alpha-chloroacrylamide, or monoalkyl substitution products thereof methyl vinyl ketone and methyl isopropenyl ketone'; vinyl .carboxylates such as vinyl acetate, vinyl chloroacetate, vinyl propionate,

and vinyl stearate; N-vinyl imides such as N-vinylphthalimide, and N-vinylsuccinimide; methyl enemalonic esters; itaconic acid and itaconic esters; trifiuorochloroethylene; N-vinylcarbazole; i-vinylpyridine, vinyliurane; butyl vinyl suli'one,

. to 1 grams per segand mtil breakage odecurs. tSg'eral deter linigailzliggs atria mafdteh at gr! t andthevauesareave urvesare en rawn o veagrap e rs one ev atempem um mg In the above table the outstanding periormance oi the dithioglycidolthe fact that at a temperature as gh as 150 C. the tensile strength mer weight when heated at C. for 24 hours under autogenous pressure in the presence of 1% of benzoyl peroxide.

The invention is not limited to any particular polymerization process or catalyst. Thus, the methods of polymerization may include (1) aqueousdispersion, (2) solution in organic solvents, including solvents which are capable of dissolving the polymer and (3) bulk. All of these processes are adequately discussed in the prior art and are familiar to skilled workers. It is to be understood that the present invention is applicable to such processes whether they are conducted batchwise or in a continuous manner. For polymerizations carried out in aqueous systems, catalysts such as ammonium or alkali metal perdisulfates are usually employed, particularly at temperatures below about 50 C. Other inorganic water-soluble catalysts which may be used in aqueous systems include hydrogen peroxide, perborates, perphosphates, percarbonates and peracetates. For polymerizations in nonaqueous systems. which ordinarily involve temperatures somewhat above 50 0., catalysts which may be employed include benzoyl peroxide, acetyl benzoyl peroxide, lauroyl peroxide, succinyl peroxide, dibutyryl peroxide, ,tertiary butyl hydroperoxide and diethyl peroxide. The rate of polymerization may also be increased by exposure of the polymerization mixture to ultra-violet light and in such cases it is advantageous to add accelerators such as benzoin or diaeetyl. In polymerizations carried out in aqueous systems, adjuvants selected from the class of inorganic sulfur compounds which yield sulfur dioxide on treatment with strong acid may be employed to assist in accelerating the.

polymerization. Such adjuvants include sodium bisulflte, sodium sulflte, sodium thiosulfate, and sodium hydrosulfite.

The concentration of modifier required to bring about the desired improvement in resistance to a 8 high temperature depends primarily on the conditions employed in the polymerization. In general, it appears desirable to approach as nearly as possible the maximum amount of dithioglycidol which can be tolerated without completely inhibiting the polymerization reaction. Although it is possible to employ from 0.01% to 2% of dithioglycidol modifier, it is preferred to use from 0.05% to 0.2% under the usual conditions.

It may be said as a general guide that, other factors being constant, the amount of modifier should be increased with increasing polymerization temperature. For example, ii 0.1% of dithioglycidol is sufiicient at a polymerization tem-- perature of 5-10 C., as much as 2% can be used at a polymerization temperature of 100 C. to give approximately the same effect. At a constant temperature, e. g. 50 C., an increase in catalyst concentration will in general require an increase in modifier concentration. For example, the use of 0.2-0.5% of ammonium perdisulfate would call for (Ll-0.2% dithioglycidol, whereas 12% of catalyst would require 0.31% of dithioglycidol.

Among the nonaqueous media, which may be employed for the production of acrylonitrile polymer are acetone, benzene, dioxan, tert.-butanol, and methanol. With all of these solvents the polymer is precipitated from solution immediately as it is formed. It is likewise possible to use solvents which dissolve the polymer to give solutions directly spinnable without intermediate isolation of the product. Such solvents include dlmethyl formamide and tetramethylene sulfone.

The polymers prepared in the presence of dithioglycidol show a considerably better color stability than unmodified polyacrylonitrile prepared under similar conditions. It has been the practice to spin polyacrylonitrile from solutions in dimethyl formamide and in order to prepare the dimethyl ,formamide solutions it is necessary to heat the mixture to about 120 C. to reach the concentration of the solids desired. In this step there is often a color change to yellow or amber which afiects the color of the spun fibers. The presence of dithioglycldol very markedly reduces the tendency to undergo discoloration under these conditions.

The polyacrylonitrile modified during polymertion with dithioglycidol is used almost excluvely for the production of fibers. Copolymers acrylonitrile with other poiymerizale comunds, may be used in such applications as the roduction or moldings, fllms, foils and coatings.

6 The fibers spun from polyacrylonitrile modified with dithioglycidol are particularly applicable to uses in which resistance to high temperature is required, such as heavy duty tires, aircraft tires,

ropes, cordage and the like.

The term monoethylenically unsaturated is used to denote the presence of one and only one carbon to carbon ethylenic, i. e. non-aromatic double bond.

Copolymers of acrylonitrile with up to 10% of a vinylpyridine form the subject of my copending application Serial No. 10,910, filed February 2. In the process of polymerizing an acrylonitrile composition wherein the polymerizable portion is substantially entirely acrylonitrile the improvement which comprises carrying out the polymerization in the presence of from 0.01. to 2%,

by weight of the acrylonitrile, of dithioglycidol,

CHz-CHCH2SH M '3. In the process of. polymerizing an aqueous acrylonitrile dispersion wherein the polymerizable portion is substantially entirely monoethylenically unsaturated and is at least acrylonitrile the improvement which comprises carrying out the polymerization in the presence of from 0.01 to 2%, by weight of the polymerizable componcuts. of dithioglycidol,

' CH:CH--0H1SH HAROLD WIIJ'RED ARNOLD.

No references cited. 

